Four strokes, four pistons, i.c. engine with toric cylinder



o. CAREDDU 3,221,716

FOUR STROKES, FOUR PISTONS, I.C. ENGINE WITH TORIC CYLINDER Dec. 7, 1965 5 Sheets-Sheet 1 Filed July 24, 1962 INVENTOR [r11 0 waflq BY A4 j/ I Dec. 7, 1965 i o. CAREDDU 3,221,716

FOUR STROKES, FOUR PISTONS, I.C. ENGINE WITH TORIC CYLINDER Filed July 24, 1962 5 Sheets-Sheet 2 Dec. 7, 1965 o. CAREDDU FOUR STROKES, FOUR PISTONS, I.C. ENGINE WITH TORIC CYLINDER 5 Sheets-Sheet 5 Filed July 24. 1962 was N M N IN VENTOR.

o. CAREDDU 3,221,716

I I.C. ENGINE WITH TORIC CYLINDER Dec. 7, 1965 FOUR STROKES, FOUR PISTONS,

Filed July 24, 1962 5 Sheets-Sheet 4 INVENTOR.

Dec. 7, 1965 FOUR STROKES, FOUR PISTONS Filed July 24, 1962 5 Sheets-Sheet 5 INVENTOR.

United States Patent 3,221,716 FOUR STROKES, FOUR PISTONS, LC. ENGINE WITH TQRIC CYLINDER Orazio Careddu, Via Borgonuovo 10, Milan, Italy Filed July 24, 1962, Ser. No. 212,761 Claims priority, application Italy, July 28, 1961, Patent 662,503 6 Claims. (Cl. 123-11) This invention relates to a rotary internal combustion engine including a toroidal cylinder having a longitudinal axis, and two pairs of pistons contained therein, the pistons in each pair being arranged diametrically opposite each other and fixedly connected to a drive shaft, diiferential gear means connected to the drive shafts for rotating therewith and control means for alternatingly locking one of the pairs of pistons.

In the attached drawings an embodiment of the present invention is shown as non-limiting example.

FIG. 1 of the drawings is a sectional view of the complete engine;

FIG. 2 is a front view of a sealing ring;

FIG. 3 is a sectional view of an oil sump for retaining the oil leaving the combustion chambers through the outlet openings;

FIG. 4 is a sectional view of the differential gear means shown in FIG. 1 showing in addition to the output shaft;

FIG. 5 is a sectional view of the sealing ring shown in FIG. 2;

FIG. 6 is a sectional view of the engine taken normal to the axis of the drive shafts and showing the piston arrangement;

FIG. 7 is a front view of a gas sealing ring;

FIG. 8 is a perspective view of another embodiment of a gas sealing ring;

FIG. 9 is a view of a blank for forming the gas sealing ring shown in FIG. 9;

FIG. 10 is a developed view of the control means of the gear means;

FIG. 11 is a sectional view taken along line XIXI of FIG. 10;

FIG. 12 is a sectional view taken along line XIIXII of FIG. 10;

FIG. 13 is a perspective view of the features shown in FIGS. 11 and 12;

FIGS. 14a-19a are schematic views of the engine showing the pistons in different respective positions; and

FIGS. 14b19b show schematically the positions of the control means at the respective piston positions shown in the respective FIGURES 14a-19a.

The hereinbelow described internal combustion engine provides two active strokes for each revolution of the driving shaft. The engine consists fundamentally of three parts; a toric cylinder with four pistons; an epicyclic train (sun-and-planet motion) and control means.

MECHANICAL FEATURES The toric cylinder consists of two parts 5, 6, FIG. 1, screwed together, and a port opened in the internal part of the cylinder provides for the access of the two driving rings 7 and 8. Each of these rings 1-4 supports two arms (or brackets) on which pistons are mounted.

Two of the four pistons are connected to each of the rings 7, 8 so that each piston connected to one ring is located between the two pistons mounted on the second parallel ring. If the pistons 1 and 2 are pistons mounted on the first ring, and pistons 3 and 4 are mounted on the second one, in working condition they work in this sequence: 1324, FIGS. 14a, 15a, 16a, etc. Two shafts 17-18, FIG. 1, coaxial and respectively integral with the two driving rings, have keyed on at their ends, two ring bevel gears (crown gears) 1011, FIG. 1.

3,221,716 Patented Dec. 7, 1965 The epicyclic train consists of two crown gears 10, 11 and three bevel gears (planetary gears) 150, FIGS. 1-4 engaging the crown gears 10 and 11 by their teeth portions 151, 152. The three planetary gears are mounted on the spur gear 154 which engages with a gear 14, FIG. 4, the last being mounted on the driven shaft 15. In addition the three planetary gears could be mounted on the idle shafts 19, FIGS. 14, thus improving their sturdiness.

The control means consists of a rocking plate mounted by means of a needle bearing 103 on arm 102 tiltable about the pivotal pin 101 and carrying on pin 104 a roller r, and cams on the faces of the gears 10, 11 which are directed against each other. Cams A A B B C and C are on gear 10 and the corresponding cams on gear 11 have been designated with the same reference to which a prime has been added. Section IV-IX, FIG. 11, shows the roller (r) (also FIG. 10) which comes into contact with the cams to be controlled thereby.

It can be seen that cam C can move only when the roller shifts a certain degree and consequently only if the rocking plate rotates a certain angle. The control cams are shown in a developed view in the drawings for easier understanding of their functioning.

OPERATION The pairs of pistons work intermittently while continuous operation of the driven shaft is achieved through the epicyclic train which by means of the three ring bevel gears transmits continuous rotatory motion to the driven shaft.

The control means controls the motion of the pairs of pistons; in other words it locks a pair and allows the other one to move. In the locked position a pair of pistons 1-2 divides the toric cylinder in two parts, FIG. 14a, whereby piston 1 separates the suction port 160 from the exhaust port 161.

The motion of the pistons and consequently of the control means is exclusively forced by the thermal energy of the gas.

The pistons rotate always in the same direction (clockwise in the drawing) and the same do the cams. FIG. 14 shows pistons 1 and 2 in stationary phase. Between pistons 1 and 3 the suction stroke is beginning; between 3 and 2 there is a compression stroke; between 2 and 4 an expansion stroke; between 4 and 1 an exhaust stroke.

FIG. 14b shows pawl-shaped cam A (on the crown gear connected to pistons 1-2) in mesh with a cutout 105 of plate 100. The force P (on A due to the force of the expanding gas on piston 2 is supported by the cam B which is part of the crown gear connected to pistons 3-4. Cam B sliding along the roller r (of the same are as pistons 3-4) prevents the rocking plate 100 from moving and thus does not allow pawl K to disengage before completion of expansion.

While the pistons 1 and 2 are locked, the pistons 3 and 4 will move and move thereby the cam B;. When the cam B' has moved relative to the roll r, as shown in FIG. 15, so that the end of this cam is still in contact with the roll, the cam C' comes into contact with the roll 4 and the profile of the cam C is formed in such a manner that this contact occurs without impact and practically noiseless. After contact between cam U and roller 4, the latter and the plate 100 on which the roller r is mounted will be tilted about the axis of the pin 101, so that the pawl-shaped cam A will be released, which frees the pair of pistons 1, 2 for rotation. At this moment, both pairs of pistons will move, that is, the pistons pairs 1, 2 will move due to the increasing compression of the gas between the pistons 2 and 3, while the piston pair 3, 4 will move due to the action of the flywheel, not shown in the drawing, so that the gas mixture compressed between the pistons 2 and 3 will come in contact with the sparkplug to be ignited thereby. While the gears 10 and 11 turn, the plate 100 will be held by the cam C, in tilted position as shown in FIG. 17 so that the pawl-shaped cam A will engage into the cutout 105 of the plate. At this moment (FIG. 18) the cam C' releases the roller 4 and the cam B tilts the plate 100 in opposite direction and locks thereby the pair of pistons 3, 4 (FIG. 19) in the same position in which the pair of pistons 1, 2 has previously been locked.

To describe one cycle of operation in further detail, it is mentioned that, as shown in FIG. 14, during the movement of the piston 4 in the direction of the arrow V under the pressure of the gas expanding in the chamber between the pistons 2 and 4, the piston 2 has the tendency to move simultaneously with the piston 4 but in opposite direction, which movement, however, is prevented by the engagement of the pawl-shaped cam A into the cutout 105 of the plate 100. The force P thus transmitted onto the cam A will be transmitted in form of a force P onto the cam B' which force will be finally absorbed by the shoulder bearing 153 shown in FIG. 1. The cam B, moves along the roller r in contact with the latter and prevents thereby a tilting of the plate 100 so that the cam A cannot disengage from the cutout 105 before the expansion of the gas is finished. FIG. 15 shows the position in which the compression in the chamber between the pistons 3 and 2 and at the same time the expansion in the chamber between the pistons 2 and 4 is nearly finished. During this part of the cycle, the pressure onto one side of the piston 2 increases continuously due to the compression of the gas, whereas the pressure on the other side of the piston 2 exerted by the expanding gas decreases continuously. The force P, which has its maximum at the beginning of the expansion continuously decreases in size (P' in FIG. 15), until this force becomes zero at the moment in which the cam B' comes out of contact with the roller r. At this moment, the pressure produced by the compressed gas on one side of the piston 2 and by the expanding gas on the other side of this piston will be in equilibrium. At the next moment, the pressure of the compressed gas will become greater than the pressure of the expanding gases, and the piston 2 will transmit onto the gear 10 a force S (FIG. 16) which has the tendency to move the cam A in direction of the arrow V so that the cam A, will have the tendency to move out of the cutout 105 of the plate 100. Due to the action of the flywheel, the cam C will continue its motion and thereby favor the tilting of the plate 100 by a small pressure N. The movement of the piston pair 3, 4 and the cams coordinated therewith is slowed down during this part of the cycle, since the compressed gas in the chamber between the pistons 3 and 2 will be ignited, whereas the movement of the piston pair 1, 2 is accelerated due to the high explosion pressure. The piston pair 1, 2 now passes fast through the are 10 (FIG. 17) and the pawl-shaped cam A will move out of the cutout 105 due to the greater value of the force S which reaches its maximum value S (FIG. 17). The roller 1' rolling along the cam is held by this cam in a position in which the plate 100 is tilted in such a manner to be ready to receive the pawl-shaped cam A' in its second cutout 105.

During the compression of the gas in the chamber between the pistons 3 and 2, the pressure on the piston 3 will continuously increase with the movement of the piston, and this pressure will at the moment of the ignition of the gas (FIG. 16) increase considerably and will attain its maximum when the piston 3 is in the position shown in FIG. 18. However, the piston 3 can move farther and overcome this pressure to move into the position shown in FIG. 19 because the flywheel will cause such a rotation.

The piston 2 continues in the meantime on its accelerated movement from the position shown in FIG. 17 to the position shown in FIG. 18, passing thereby through the are He, which is equal to the path which the cam B has to travel to come in contact with the roller r. It should be noted that the two arcs I0 and 11a are equal to the are 1 (FIG. 18) and the piston 2 drives therefor the flywheel while the piston 3 moves to its rest position.

The pawl-shaped cam A' which moves with decreasing speed now becomes located in the cutout of the plate 100 while the cam C; releases the roller r and permits tilting of the plate 100 under the influence of the cam B After such tilting, the gear 11 and the pair of pistons 3, 4 coordinated therewith are locked while the pistons 1, 2 are free to turn.

It may be seen from the schematic FIGS. 14 -19 that this engine does not need any inlet and outlet valves, since the pistons 1-4 themselves lead the gas flow through inlet openings into the correct combustion chamber and the burned gases out of the combustion chamber through outlet openings 161. A sparkplug 162 may be employed as ignition means. It is located opposite of outlet openings 161 inside a recess 164 of the cylinder wall having an opening communicating with the combustion chamber 163. The sparkplug is connected to a regular electric system as used for conventional piston engines. It provides a spark at the electrodes of the sparkplug whenever a compression stroke has been finished.

Seal.-The gas sealing rings for pistons are identical to normal piston sealing rings while seal between driving rings and toric cylinder is achieved by means of graypig iron, trapezoidal section, gas sealing rings 140 (FIGS. 1, 2 and 5).

These gas sealing rings are properly located in spaces between the driving rings 7 and 8 and their adherence in these spaces is caused by the difference between external thrust T, FIG. 15b (elastic reaction of the ring) and internal thrust T (pressure of gas). If the surface of gas sealing ring exposed to gas pressure is 0.5 x 60 mm. and the M.E.P. is 10 kg./mm. the internal thrust will be 1 kg. The external thrust will be of 4 kg. and thus adherance results 1 kg. If the lateral surface of one gas sealing ring amounts to 100 mm. specific pressure will be 5 grams/mm. a very reasonable one.

FIG. 2 shows a Seinger type gas sealing ring. With this type of gas sealing ring the external thrust is the reaction of the elastic ring itself.

FIG. 7 shows another type of gas sealing ring 141, which needs the spring 143 to give external thrust. This spring, made of steel sheet, is sheared and folded as shown in FIGS. 89. Every gas sealing ring may be in contact with antifriction metal and can have radial channels 142 for improving the lubrication as shown in FIG. 5.

RECAPITULATION Each pair of pistons rotates for (active stroke) and then stops. The rotatory motion is transmitted to cams (through half-shafts 17 and 18, FIG. 1) which are controlled by to rocking plate 100 and roller r. This arrangement locks and releases the pairs of pistons alternatingly, so controlling the stroke sequence. The intermittent motion of pistons is converted in a continuous motion by the epicyclic train.

When a pair of pistons is in locked position also its half-shaft and its ring bevel gears are locked. But that crown gear connected to the pistons in motion (active stroke) will move the three planetary gears and the spur gear as well. The spur gear is in continuous rotatory motion because of planetary gears presence.

A flywheel is mounted on the driven shaft 15 together with spur gear 14, FIG. 4, but is not shown on the drawings. Shafts 18 and 17 are turnably mounted in housing 5, 6 by self-regulating bearings 130, 131, respectively, in which the gas sealing rings 132, 133 press the brass sleeves 134, 135 in axial direction keeping the two shafts 17, 18 absolutely coaxial. At the other end, the two shafts 17, 18 are mounted by ball bearing 155 respectively roller bearing 153.

' LUBRICATION The lubrication oil flows (white arrows) through the hollow shaft 18, enters the channels 13 of the arms 21 (black arrows) and passes through a bore 12, FIG. 6 goes to lubricate the cylinder wall 3. The piston being stiifiy mounted on the bracket does not contact the wall 23 of the toric cylinder leaving a clearance of 0.05 mm.

In this interspace piston rings 24 and wiper rings 25 are located. These wiper rings remove the oil in excess which is absorbed through the holes 20, FIG. 1 and then conveyed to a gear pump through a bore 22, FIG. 1. Should a portion of oil not be recovered as hereinbelow described and discharged out through exhaust port 161, it can be recovered by means of a simple siphon collector as shown in FIG. 3, the outlet opening 165 of which is connected to the oil pump by a pipe not shown in the figures.

The nature of my invention having now been particularly described, I declare that what I claim is:

1. In a rotary internal combustion engine comprising, in combination, stator means including a toroidal cylinder having a longitudinal axis; rotor means mounted in said stator means turnable about said axis, said rotor means including two pairs of pistons and a pair of drive shafts coaxial with said axis of said cylinder and respectively connected to said pairs of pistons for rotation therewith, the pistons in each pair being diametrically opposite each other and fixedly connected to each other,

said pistons being rotated in said cylinder and dividing the same into four chambers; differential gear means including a pair of side gears respectively connected to the drive shafts for rotation therewith; and control means located between said side gears for alternatingly locking one of said side gears while the other rotates through a given angle, said control means comprising a single locking member located between said side gears movable between a first locking position inwhich said locking member is in locking engagement with one of said side gears for preventing rotation of said one side gear about said axis and a second locking position in which said locking member is in locking engagement with the other side gear for preventing rotation of the latter about said axis, and means on said side gears for holding said locking member in said first locking position as said other side gear and the drive shaft and pistons connected thereto rotate through said given angle and for moving said locking member into said second locking position as said other side gear finishes rotation through said given angle so as to alternatingly lock one of said side gears and the drive shaft and the pair of pistons connected thereto while the other side gear and drive shaft and pistons connected thereto rotate through said given angle.

2. In a rotary internal combustion engine comprising, in combination, stator means including a toroidal cylinder having a longitudinal axis; rotor means mounted in said stator means turnable about said axis, said rotor means including two pairs of pistons and a pair of drive shafts coaxial with said axis of said cylinder and respectively connected to said pairs of pistons for rotation therewith, the pistons in each pair being diametrically opposite each other and fixedly connected to each other, said pistons being rotated in said cylinder and dividing the same into four chambers; differential gear means including a pair of side gears respectively connected to the drive shafts for rotation therewith; and control means located between said side gears for alternatingly locking one of said side gears while the other rotates through a given angle, said control means comprising a single locking member located between said side gears and being mounted for swinging movement between a first locking position in which said locking member is in locking engagement with one of said side gears for preventing rotation of said one side gear about said axis and a second locking position in which said locking member is in locking engagement with the other side gear for preventing rotation of the latter about said axis, and means on said side gears for holding said locking member in said first locking position as said other side gear and the drive shaft and pistons connected thereto rotate through said given angle and for moving said locking member into said second locking position as said other side gear finishes rotation through said given angle so as to alternatingly lock one of said side gears and the drive shaft and the pair of pistons connected thereto while the other side gear and drive shaft and pistons connected thereto rotate through said given angle.

3. In a rotary internal combustion engine comprising, in combination, stator means including a toroidal cylinder having a longitudinal axis; rotor means mounted in said stator means turnable about said axis, said rotor means including two pairs of pistons and a pair of drive shafts coaxial with said axis of said cylinder and respectively connected to said pairs of pistons for rotation therewith, the pistons in each pair being diametrically opposite each other and fixedly connected to each other, said pistons being rotated in said cylinder and dividing the same into four chambers; difierential gear means including a pair of side gears respectively connected to the drive shafts for rotation therewith; and control means located between said side gears for alternatingly locking one of said side gears while the other rotates through a given angle, said control means comprising a single locking plate mounted for swinging movement between said side gears, a pair of male locking means and a pair of female locking means, one of said pair of locking means provided on said side gears, respectively, and the other of said locking means provided on said locking plate, said locking plate being movable between a first locking position in which one of said locking means on said locking plate engages with the locking means on one of said side gears for preventing rotation of said one side gear about said axis and a second locking position in which the other locking means on said locking plate is in locking engagement with the locking means on the other side gear for preventing rotation of the latter about said axis, and means on said side gears for holding said locking plate in said first locking position as said other side gear and the drive shaft and pistons connected thereto rotate through said given angle and for moving said locking plate into said second locking position as said other side gear finishes rotation through said given angle so as to alternatingly lock one of said side gears and the drive shaft and the pair of pistons connected thereto while the other side gear and drive shaft and pistons connected thereto rotate through said given angle.

4. In a rotary internal combustion engine comprising, in combination, stator means including a toroidal cylinder having a longitudinal axis; rotor means mounted in said stator means turnable about said axis, said rotor means including two pairs of pistons and a pair of drive shafts coaxial with said axis of said cylinder and respectively connected to said pairs of pistons for rotation therewith, the pistons in each pair being diametrically opposite each other and fixedly connected to each other, said pistons being rotated in said cylinder and dividing the same into four chambers; differential gear means including a pair of side gears respectively connected to the drive shafts for rotation therewith; and control means located between said side gears for alternatingly locking one of said side gears while the other rotates through a given angle, said control means comprising a single locking plate mounted for swinging movement between said side gears and being formed with a pair of opposite cutouts, a pair of projections respectively formed on said side gears for locking engagement with said cutouts,

respectively, said locking plate being movable between a first locking position in which the projection on one of said side gears lockingly engages into one of said cutouts in said locking plate for preventing rotation of said one side gear about said axis and a second locking position in which the projection on the other side gear lockingly engages into the other cutout of said locking plate for preventing rotation of said other side gear about said axis, and means on said side gears for holding said locking plate in said first locking position as said other side gear and the drive shaft and pistons connected thereto rotate through said given angle and for moving said locking plate into said second locking position as said other side gear finishes rotation through said given angle so as to alternatingly lock one of said side gears and the drive shaft and the pair of pistons connected thereto while the other side gear and drive shaft and pistons connected thereto rotate through said given angle.

5. In a rotary internal combustion engine comprising, in combination, stator means including a toroidal cylinder having a longitudinal axis; rotor means mounted in said stator means turnable about said axis, said rotor means including two pairs of pistons and a pair of drive shafts coaxial with said axis of said cylinder and respectively connected to said pairs of pistons for rotation therewith, the pistons in each pair being diametrically opposite each other and fixedly connected to each other, said pistons being rotated in said cylinder and dividing the same into four chambers; differential gear means including a pair of side gears respectively connected to the drive shafts for rotation therewith; and control means located between said side gears for alternatingly locking one of said side gears while the other rotates through a given angle, said control means comprising a single locking plate mounted for swinging movement between said side gears and being formed with a pair of opposite cutouts, a pair of projections respectively formed on said side gears for locking engagement with said cutouts, respectively, said locking plate being movable between a first locking position in which the projection on one of said side gears lockingly engages into one of said cutouts in said locking plate for preventing rotation of said one side gear about said axis and a second locking position in which the projection on the other side gear lockingly engages into the other cutout of said locking plate for preventing rotation of said other side gear about said axis, and cam means on said side gears for holding said locking plate in said first locking position as said other side gear and the drive shaft and pistons connected thereto rotate through said given angle and for moving said locking plate into said second locking position as said other side gear finishes rotation through said given angle so as to alternatingly lock one of said side gears and the drive shaft and the pair of pistons connected thereto while the other side gear and drive shaft and pistons connected thereto rotate through said given angle.

6. In a rotary internal combustion engine comprising, in combination, stator means including a toroidal cylinder having a longitudinal axis; rotor means mounted in said stator means turnable about said axis, said rotor means including two pairs of pistons and a pair of drive shafts coaxial with said axis of said cylinder and respectively connected to said pairs of pistons for rotation therewith, the pistons in each pair being diametrically opposite each other and fixedly connected to each other, said pistons being rotated in said cylinder and dividing the same into four chambers; differential gear means including a pair of side gears respectively connected to the drive shafts for rotation therewith; and control means located between said side gears for alternatingly locking one of said side gears while the other rotates through a given angle, said control means comprising a single locking plate mounted adjacent one end for swinging movement about a swinging axis substantially normal to said longitudinal axis, roller means carried by said plate in the region of the other end thereof projecting therefrom parallel to said swinging axis, a pair of opposite cutouts formed in said plate in the region of said one end thereof, and a pair of projections respectively formed on said side gears for locking engagement with said cutouts, respectively, said locking plate being swingable about said swinging axis between a first locking position in which the projection on one of said side gears lockingly engages into one of said cutouts in said locking plate for preventing rotation of said one side gear about said axis and a second locking position in which the projection on the other side gear lockingly engages into the other cutout of said locking plate for preventing rotation of said other side gear about said axis, first cam means on each side gear and cooperating with said roller means for holding said plate in said first locking position as said other side gear and the drive shaft and pistons connected thereto rotate through said given angle, and second cam means on each of said side gears and cooperating with said roller means for swinging said plate to said second locking position as said other side gear finishes rotation through said given angle so as to alternatingly lock one of said side gears and the drive shaft and the pair of pistons connected thereto by the other side gear and drive shafts and pistons connected thereto rotate through said given angle.

References Cited by the Examiner UNITED STATES PATENTS 987,929 3/1911 Thomas 12311 1,318,017 10/1919 Shank 123-11 1,568,053 l/ 1926 Bullington 12311 1,676,211 7/ 1928 Bullington 123-11 1,944,875 1/1934 Bullington 12311 1,962,408 6/1934 Powell 123--11 1,994,858 3/1935 Lack et a1 12311 2,092,254 9/1937 Horner 12311 2,124,327 7/1938 Wolstenholme 12311 2,638,880 5/1953 Mallinckrodt 123-1l 2,657,676 11/ 1953 Mallinckrodt 12311 2,680,430 6/1954 Mallinckrodt 12311 2,734,489 2/1956 Tschudi 123-11 SAMUEL LEVINE, Primary Examiner.

LAURENCE V. EFNER, KARL J. ALBRECHT,

Examiners. 

1. IN A ROTARY INTERNAL COMBUSTION ENGINE COMPRISING, IN COMBINATION, STATOR MEANS INCLUDING A TOROIDAL CYLINDER HAVING A LONGITUDINAL AXIS; ROTOR MEANS MOUNTED IN SAID STATOR MEANS TURNABLE ABOUT SAID AXIS, SAID ROTOR MEANS INCLUDING TWO PAIRS OF PISTONS AND A PAIR OF DRIVE SHAFTS COAXIAL WITH SAID AXIS OF SAID CYLINDER AND RESPECTIVELY CONNECTED TO SAID PAIRS OF PISTONS FOR ROTATION THEREWITH, THE PISTONS IN EACH PAIR BEING DIAMETRICALLY OPPOSITE EACH OTHER AND FIXEDLY CONNECTED TO EACH OTHER, SAID PISTONS BEING ROTATED IN SAID CYLINDER AND DIVIDING THE SAME INTO FOUR CHAMBERS; DIFFERENTIAL GEAR MEANS INCLUDING A PAIR OF SIDE GEARS RESPECTIVELY CONNECTED TO THE DRIVE SHAFTS FOR ROTATION THEREWITH; AND CONTROL MEANS LOCATED BETWEEN SAID SIDE GEARS FOR ALTERNATINGLY LOCKING ONE OF SAID SIDE GEARS WHILE THE OTHER ROTATES THROUGH A GIVEN ANGLE, SAID CONTROL MEANS COMPRISING A SINGLE LOCKING MEMBER LOCATED BETWEEN SAID SIDE GEARS MOVABLE BETWEEN A FIRST LOCKING POSITION IN WHICH SAID LOCKING MEMBER IS IN LOCKING ENGAGEMENT WITH ONE OF SAID SIDE GEARS FOR PREVENTING ROTATION OF SAID ONE SIDE GEAR ABOUT SAID AXIS AND A SECOND LOCKING POSITION IN WHICH SAID LOCKING MEMBER IS IN LOCKING ENGAGEMENT WITH THE OTHER SIDE GEAR FOR PREVENTING ROTATION OF THE LATTER ABOUT SAID AXIS, AND MEANS ON SAID SIDE GEARS FOR HOLDING SAID LOCKING MEMBER IN SAID FIRST LOCKING POSITION AS SAID OTHER SIDE GEAR AND THE DRIVE SHAFT AND PISTONS CONNECTED THERETO ROTATE THROUGH SAID GIVEN ANGLE AND FOR MOVING SAID LOCKING MEMBER INTO SAID SECOND LOCKING POSITION AS SAID OTHER SIDE GEAR FINISHES ROTATION THROUGH SAID GIVEN ANGLE SO AS TO ALTERNATINGLY LOCK ONE OF SAID SIDE GEARS AND THE DRIVE SHAFT AND THE PAIR OF PISTONS CONNECTED THERETO WHILE THE OTHER SIDE GEAR AND DRIVE SHAFT AND PISTONS CONNECTED THERETO ROTATE THROUGH SAID GIVEN ANGLE. 